Method of expanding pistons



Dec. 11, 1934. R MUNDT METHOD OF EXPANDING PISTONS Original Filed May 9,1932 Patented Dec. 11, 1934 UNITED STATES METHOD OF EXPANDING PISTONSRobert Mundt, Cedar Rapids, Iowa Original application May 9, 1932,Serial No.

610,198. Divided and this application February 25, 1933, Serial No.658,555

3 Claims.

This invention relates to methods of forming pistons and has particularrelation to a method of expanding pistons so that they will be a closerunning fit in the cylinders with which they are to be used.

The present application is a division of my 00- pending applicationSerial Number 610,198 filed May 9th, 1932, and covering an invention indevices for expanding pistons.

I have observed, and it is well known in the art, that pistons ofinternal combustion engines, compressors and the like become loose andworn in service so that loss of compression results and piston slapdevelops. Even in new engines the pistons are sometimes poorly fitted,and by the methods known to the prior art would, of necessity, have tobe replaced in order to secure a properly functioning motor.

I have observed that most pistons are constructed with oppositelydisposed openings in the side walls thereof below the piston rings andthat in most cases the skirt of the piston is provided with one or moreslots to take care of differential expansion of the cylinder and piston.The side walls of the piston are held or reinforced by means of strutswhich extend across the openings before mentioned and the bosses inwhich the piston pins are located constitute parts of these struts. Thestruts are usually provided with one or more openings on each side ofthe piston pin boss, presumably in order to lighten the weight of thepiston.

I have devised a means for and a method of expanding the struts and theskirt of the piston so that the diameter of the piston may be increasedsufiiciently that it may be made a close running fit in the cylinderwith which it is to be used. :The circumference of the piston islikewise increased and the expansion throughout may be controlled inminute, sharply-defined, increments so that accurate fitting of thepiston may be secured.

An object of my invention'is to provide means of, and a method for,expanding a piston to any desired diameter and circumference.

Another object of, my invention is to provide a means for closelycontrolling the process of expanding a piston.

Another object of my v invention is to: provide 'a relatively simple,eiiicient, and inexpensive device for expanding pistons.

Other and further features and objects of my invention will be moreapparent to those skilled in the art upon a consideration of theaccompanying drawing and following specification, wherein is disclosedseveral exemplary embodiments of the invention, with the understanding,

however, that such changes may be made therein as fall within the scopeof the appended claims without departing from the spirit of theinvention.

In the drawing and in the following specification there will bedescribed several devices embodying means for practicing my improvedmethod of expanding pistons.

Figure 1 is a side elevational view of the piston expanding device. Thepiston has been shown in dotted lines to illustrate theposition itoccupies while it is being expanded.

Figure 2 is a view in front elevation of'a device which may be locatedin the vertically-extending, slideably-engaged plunger which is utilizedfor applying'pressure to expand the piston.

Figure 3 is a View in side elevation of the piston,

the mandrels, and a portion of the plunger, and shows the piston in theposition it occupies while the device is being used to expand the skirtof the piston.

' Figure 4 is a View in side elevation of a portion of the standard, ofthe piston, shown in dotted lines, and of the mandrels used in expandingthe struts of the piston.

Figure 5is a View in perspective of a mandrel constructed according toan embodiment of my invention, and

Figure 6 is a view in elevation of a pair of mandrels constructedaccording to an embodiment of my invention.

Referring now to the drawing and particularly 'to' Figure 1 thereof,there is shown at 10 a base,

substantially rectangular in shape, and having an upthrust centralportion 11 provided with a suitably-shaped, rectangular opening 12 inwhich astandard 13 may be located. The base 10 may be secured to asuitable support 14 such as a table or the like by means of bolts 16. Ofcourse,

] the base may be held in a vise or similar clamp if desired.

The cross-sectional shape of the standard 13 is immaterial but theopening 12 in the base must correspond to the shape of the lower end ofthe standard in order that the standard will be a tight'fit in the base.In the present instance, however, I prefer to utilize a standard whichis substantially rectangular in cross-section so that it may be fastenedin a vise or the like without the necessity of using a base. The objectof this construction, of course, is to permit the standard to be used asdesired either in connection with a base which is permanently located ona work bench, or as a toolwhich may be used in connection with Vises orother clamping devices which are available in a shop.

The standard 13 includes an upright portion 15 and ahorizontally-extending jaw portion 17. A horizontally-extending guide 18is a part of the standard 13 or is secured to it in a suitable manner asby means of bolts or the like. A lower jaw 33, hereinafter moreparticularly described, is also a part of the standard13 or is securedto it in any suitable manner.

The upper jaw 17 has a vertically extending slot 19, preferablyrectangular in shape, near its outer end, and the jaw is provided witha'pair of depending guides 21 and 22 whichare malignment with the slot19. A pair of links 24 are pivotally engaged to the upper jaw 17 bymeans of a bolt or pivot-pin 25 and the link '24 is free1to move througha limited are for a purpose hereinafter explained. A plunger 26 isdisposed Within the slot 19 at the end of the jaw 17 and extendsdownwardlythrougha corresponding open- .ing "2.7 in the 1 lower .guide:18.

A lever 28 is pivotally attached $170 :the link :24 as by means of abolt or pivot-pin 29, and'to the plunger 26 as by meansof a bolt orpivotpin 31.

In a preferred embodimentof the invention-the outer end of the .lever.28 is formed in circular cross-section and apipe extension handle :32:may be slippedon over thexend of therleverzto permit a long :lever armto be used. It may readily be understood that the length of the leverarm .28 may be sufiicientlygreat thatyby reason of the short distancebetween the pivots :29 and 31,. a very appreciable pressure may bebrought to bear upon the .plunger 26. Since :the plunger .26 :cannotmove sidewise because it .is confined by-the slots 19 and 27, therlinks-24pivot about on :pivot pin .to ,accommodatethe changinghorizontal component of the lever arm between .pivots .29

and 31.

The horizontally-extending jaw 33 .is secured to, or is -,a part of, thestandard l'3aandaffords a rest or anvil on which the piston :34 may beplaced. The outer end of the jaw .33 is drilled with-a downwardlyextending opening .36 inorder that :a cone-shaped mandrel :37 :having.131 cylindrical stem portion, may be inserted in the opening.

The mandrel 37 maybe in the shape of a truncated cone as shown inFigural or maybe a full cone as shown at 37a in Fig-ure according towhether the strut or the skirt .is to .be expanded. A recess .38ispr-ovided in-the .lowerendof the plunger 26 in order to accommodate.thehead .or tip of the mandrel 3'] when theplunger is pressed down onthe piston strut. An adapter 39, shown in Figure 3, may be inserted inrecess 38 in the end of the plunger when desired.

Most of the pistons of-the present-day art are comprised of a light head41, shown best in Figure 3, and a barrel portion 42 having a thin skirtportion 43 at the lower end thereof. A pair of oppositely-disposed,substantially-rectangular openings .44 are provided in the barrelportion. of the piston and. depressed tongues 46 extend from the head tothe skirt of the-piston. This .portion of the piston does not ordinarilymake contact with the cylinder walls. A pair of struts 47 extend acrossthe openings 4.4 at right angles to the tongues 46 and the struts arerigidly attached to or are a part of the opposite parts. of thebarrel-42.

A boss 48 in each of the tongues 46 affords means for pivotally securinga piston pin 49 to the piston, anda connecting rod 51 is attached to thepin 49 at its mid-portion, between the tongues 46. The strut 47 isprovided with one or more openings 52 on each side of the tongue 46,presumably for lightening the piston. The struts 47 determine thespacing apart of the walls of the barrel 42 as lengthening or shorteningof the struts 47 changes the diameter of the barrel portion of thepiston.

My inventionmakes use ofthe described piston construction andparticularly the strut structure for increasing the diameter and hencethe circumference of the barrel portion of the piston. It maybereadilyunderstood that by inserting the cone-shaped-mandrel 37 in the openings52 and applying pressure on the strut by means of the plunger-26'the=openings 52 may be expanded and thegportionsof the strutsadjacent to the openings stretched to increase the efiective length ofthe :struts.

If the diameter of the cylinder to which the piston belongs isaccurately determined the various open'ings '52 may be each expandedslightly and in -successionto expand the piston. If micrometermeasurements of the piston are made during this expanding process thepiston maybe expanded to any desired dimension, within reasonablelimits'and the expanding process closely controlled so that it will be aclose running fit Within the cylinder in which it isto be used. The jaw33 is sufliciently narrow that the connecting rod .5'l may be :left inthe'piston during the expanding process-and the connecting rod placedfirston one side of .the jaw and then on theother to permit :the strutsto be expanded.

It is sometimes quite desirable to expand the skirt 43 of the piston aswell and this is acconn -plished by removing the truncated-cone mandrel3'7 and replacing it with the coneeshaped mandrel 37a, which-may beeither :a relatively sharp point or may be slightlye'long-ated like asmall chisel such :as the mandrel 37b shown in'Figure '5. An adapter 39,which is provided with a flat lower face, and astem portion adapted to'be'inserte'd in the recess 39 of the plunger 26, is located in theplunger. The piston may then be placedbver the "end 'of'the {Ia-W33 'toa depth determined by a U-shaped stop 53 which is clamped to the jaw 33as by means of a 'thumb screw be. The stop accurately determines theposition of the edge of the skirt of the piston with reference 'to themandrel 37a and when the plunger 26 is brought down against thef-aoe ofthe piston "the'point of .the-cone shaped mandrel 37a is driveninto theinner wall of the skirt '43 to dent it andslightly expand the skirt atthe point where the pressure is applied. I

By'slowly rotating the piston and drivingthe mandrel-37a into the innerwall thereof at successive points a series of open'ings or dents aremade in the-inner wall. The effect of this op- 'eration is tostretch'the materialof the skirt of the piston at the-points wherepressure is applied so that when the series of dents have been madeentirely around the skirt of the piston it will be found that itsdiameter and circumference have been increased. The operation may berepeated until the skirt-is of the required size. This same operationmaybe applied to other parts of the piston such as the struts and finsin order to stretch them also.

Ihave found that it is possible to increase'the diameter of both thebarrel and the skirt of a piston as much as 20/1000 of an inch, which isamply sufiicient'in the great majority of cases to take care of almostany degree of wear in a piston. Although the piston may be expanded toeven a greater extent than 20/1000 of an inch, as a matter of practiceif the piston needs to be expanded to a greater extent than this I havefound it desirable to substitute a new piston for the worn one.

While the diameter of the piston may be readily increased, I have foundit desirable that each strut opening or each part of the skirt of thepiston should be expanded to substantially the same degree andtherefore, in another embodiment of my invention, shown in Figure 2, Ihave utilized a pressure-indicating device 56 in the plunger 26. Theplunger is of course of two parts 26a and 26b, with the part 26aslidably engaged in the part 26b so that it may move in and out withreference thereto. A spring (not shown) is interposed between parts 26aand 26b in accordance with well-known practice. The pressure-indicatingdevice 56 may be any of the types well known in the art and one part ofthe device engages the portion 26a and another part of the deviceengages the portion 261) so that when pressure is applied on the plunger26 by means of the lever arm 28 the needle 57 is moved over the scale 58of the indicator 56 to indicate the degree of pressure applied. Ifpressure is applied to the lever 28 until the needle reaches the sameposition on the dial 58 at each successive application of pressure tothe piston, then the parts of the piston, Whether they are the struts orthe skirt, will be uniformly stretched or expanded.

My method of expanding may be applied to all parts of the piston. Thepointed mandrels 37a and 371) may be applied by pressure to the skirt,the barrel, and the struts to expand any part of the piston as desiredby denting the parts and thus stretching the metal about the dent. Thetip 37b has a chisel-like point but the stretching and expanding actionis substantially the same as that secured by the pointed mandrel 37a,that is, the metal about the point of application of the mandrel isslightly displaced and stretched. When the mandrel 37b is employed thestretching action is extended along a line instead of occurring about apoint and thus a given area of metal may be stretched more in onedirection than in another.

I sometimes prefer to utilize the blunt type of mandrels shown in Figure6. The upper mandrel 390 is substantially the same as the mandrel 39 butis preferably slightly concaved at its lower face. The mandrel 37cemploys the same stem as the mandrels 37a and. 37b but the upper part ofthe mandrel is substantially the same as the lower part of the mandrel390 except that its upper surface is preferably convex. In using theblunt mandrels the mandrels 39c and 3'70 are placed in the plunger 26and the lower jaw 33, and the skirt 43 or other part to be stretched isplaced between the mandrels and pressure applied. When pressure isapplied the skirt tends to move to the position shown by the dottedlines thus stretching the metal on the inner part of the skirt and thusexpanding the piston.

It may readily be understood that I have provided a means for uniformlyand accurately expanding the barrel, struts, and skirt of the piston andthat the degree of expansion may be quite accurately controlled. Thedevice is quite simple in construction and is reliable and eflicient inoperation.

Although I have described several preferred embodiments of my inventionit is apparent that modifications may be made by those skilled in theart. For instance the location of the mandrel may be changed as desiredand it may be located in the end of the plunger. The mandrels may bequite dull at their ends or may be formed in a dull chisel-like tip, butthe method of enlarging the piston is substantially the same, that is,the piston is enlarged by stretching the skirt, struts, fins, barrel andother parts thereof. The location of the lever arm may or in fact anysuitable reversal of parts from that described may be used. These andsuch other modifications as may occur to those skilled in the art may bemade without departing from the spirit and scope of the invention as setforth in the appended claims.

Having thus described my invention, what I desire to secure by LettersPatent is:

1. The method of expanding a piston comprising stretching the strutsthereof by making openings in the struts thereof and driving theopenings in the struts onto a mandrel.

2. The method of expanding a piston having struts therein for connectingthe sides thereof comprising providing openings through the struts andexpanding the struts as desired by driving a pointed mandrel into theopenings and against the walls thereof.

3. A method of expanding a piston comprising providing openings anddriving a mandrel into the openings to expand the metal about theopenings.

ROBERT MUNDT.

also be changed in the part to be expanded

